Direct observation of room-temperature out-of-plane ferroelectricity and tunneling electroresistance at the two-dimensional limit

Authors

H. Wang, National University of Singapore
Z R. Liu, Zhejiang University
H. Y. Yoong, National University of Singapore
Tula R. Paudel, University of Nebraska-Lincoln
J. X. Xia, National University of Singapore
R. Guo, National University of Singapore
W. N. Lin, National University of Singapore
P. Yang, National University of Singapore
J. Wang, National University of Singapore
G. M. Chow, National University of Singapore
T. Venkatesan, National University of Singapore
Evgeny Y. Tsymbal, University of Nebraska-LincolnFollow
H. Tian, National University of Singapore
J. S. Chen, National University of Singapore

Date of this Version

8-20-2018

Citation

Nature Communications 9, 3319 (2018).
DOI: 10.1038/s41467-018-05662-y

Comments

Copyright 2018 Springer Nature Publishing AG. Used by permission.

Abstract

Out-of-plane ferroelectricity with a high transition temperature in nanometer-scale films is required to miniaturize electronic devices. Direct visualization of stable ferroelectric polarization and its switching behavior in atomically thick films is critical for achieving this goal. Here, ferroelectric order at room temperature in the two-dimensional limit is demonstrated in tetragonal BiFeO₃ ultrathin films. Using aberration-corrected scanning transmission electron microscopy, we directly observed robust out-of-plane spontaneous polarization in one-unitcell-thick BiFeO₃ films. High-resolution piezoresponse force microscopy measurements show that the polarization is stable and switchable, whereas a tunneling electroresistance effect of up to 370% is achieved in BiFeO₃ films. Based on first-principles calculations and Kelvin probe force microscopy measurements, we explain the mechanism of polarization stabilization by the ionic displacements in oxide electrode and the surface charges. Our results indicate that critical thickness for ferroelectricity in the BiFeO₃ film is virtually absent, making it a promising candidate for high-density nonvolatile memories.